Weighing sensors used for rotary filling heads are advantageously arranged in the shape of a circle, wherein an attempt is made to place a maximum of weighing cells on the smallest possible divided circle. This circular arrangement of weighing sensors saves installation space.
In the beverage industry, rotary filling heads are known, for example, according to DE 20304296 U, in which numerous filling stations are arranged in a circle, and very high product throughputs can be achieved due to the continuous filling. These filling machines have a filling head with a flow-rate controller, which apportions the desired quantity of fill material.
For free-flowing bulk goods, volume rotary filling heads are known. The filling head is pre-set according to the density of the fill material and directs a constant volume into the corresponding filling container. The disadvantage of these filling systems lies in the variation in density of the supplied products. Detergents can be fed, e.g., from the silo or directly from the flocculation to the filling system, and thus can have a different density due to the different pile heights. Furthermore, the construction of the volumetric filling heads limits the volume ranges and thus the weight ranges of the fill material, i.e., such systems can operate only with a limited measurement range. Volumetric rotary filling heads usually have a downstream check scale, which checks the fill weight of the packages and adjusts the filling head quantity accordingly. The disadvantage of these filling systems lies in the check weighing process, which is relatively far removed from the actual filling process and which is associated with greater waste of product with incorrect weight due to the time lag of the downstream check scale.
According to the state of the art, rotary filling heads are known which are based on the DMS weighing technique. This shows the disadvantage of the long settling time of the DMS weighing cell upon load input. This property is amplified by the rotation of the entire filling head. In addition, DMS weighing cells exhibit deflection under increasing load, which must be corrected in the state of the art with, for example, an additional correction cell (DE 372 78 66 C2).
For installation of the weighing technology in the head of a rotary filling machine with a basic circular construction, problems arise due to the installation relationships of a measurement cell. Weighing cells that are common according to the state of the art have a cuboid housing. For introduction into a divided circle, one can see that the smallest possible divided circle diameter is strongly limited by the geometric form of the measurement cell.
The weighing cells according to the state of the art shown in EP 1 409 971 with a wide fixed linkage and a trapezoidal parallelogram guidance are not suitable for accommodation in a divided circle.
EP 518202 B1 discloses a weighing sensor in which the individual functional units of the block system are implemented by means of thin sections. The figures show a weighing sensor with a narrow construction, but again there is the problem that the force-compensating magnet system represents the greatest width of the system, and this lies opposite the load-receiving side as is known in the state of the art. The diameter of the divided circle is also here definitively defined by the magnet arrangement.
The length dimensions of the weighing cells produce another disadvantage. The state of the art demonstrates weighing cells that have a parallelogram-guidance load receiver, wherein there are elastic linkages between the upper and lower parallelogram arms that reduce the magnitude of an applied force. The state of the art here demonstrates different weighing sensors with up to four force-converting stages, wherein systems with very high force-conversion ratios up to 1500:1 are to be found primarily in static applications.
The weighing sensors known according to the state of the art are constructed with a compensation lever that is extended up to the compensation system. In the case of electromagnetic force compensation, this is a system consisting of a coil and a permanent magnet system. The magnet is arranged, as described, e.g., in DE 19923207 C1, behind the force-reducing linkages. Among other things, the upper and lower parallelogram arms for the moving load receiver are constructed on the fixed part.
For monolithic weighing systems manufactured by machining, the state of the art is represented by an arrangement of load receivers, force converting levers, stationary base elements, and magnet systems lying spatially one behind the other. Furthermore, the state of the art shows us a magnet surrounded by block material, in order to achieve high measurement accuracy of the system. Such a system is not suitable for a circular arrangement with the goal of smallest possible diameter of the divided circle. A construction with a magnet arranged between the two parallelogram carriers (e.g., in DE 3243350 C2) can indeed have a space-saving arrangement, but the lever principle and the limited force conversion ratio of the system in this arrangement limits the use to a very limited weight range.
For suitability of a weighing sensor according to the principle of electromagnetic force compensation in a circular arrangement, the construction of the narrowest possible form for the weighing cell is essential. The disadvantage of such a construction lies in the weakening of the Roberval-type linkages with respect to torsion perpendicular to the introduction of force in the transverse direction of the block system. From the state of the art, it is known that monolithic weighing sensors between the load receiver and the first lever (and the other force converting levers) are advantageously constructed with a coupling element consisting of an intermediate bar and two thin sections. Furthermore, an advantageous design in the state of the art has involved constructing a thin section in the first coupling rod in the longitudinal direction of the load receiver, in order to avoid torsional moments on the force converting lever. As an example here, the publication EP 291 258 A2, especially FIG. 2, can be referenced.
The combination of narrow Roberval-type linkages (for forced parallel guidance of the load receiver) and the cited thin section leads to a less torsion-resistant weighing sensor in case of eccentric force introduction in the transverse direction of the block. Therefore, in EP 1550849A2 it was mentioned to construct the parallelogram arms accordingly wider than the block system, which represents a considerable added expense relative to the original, primarily two-dimensional weighing sensor.
DE 200 07 781 U1 discloses a weighing sensor with several force converting levers, in which a calibration weight can be selectively lowered onto or raised from a lever section. As long as the calibration weight is not being used, it can be pushed by mean of a separate lifting mechanism against the base element constructed as a stationary base, which then acts as a stop.